1. Movement speed decays when you pass certain values, it is to discourage stacking MS items. That's why you're seeing less than +50
2. Their are some very small discrepancies in the targeting indicators for abilities. Designers sometimes make them smaller than what they actually are.
3. That sounds like a bug, are their any other details you can share?
4. I'm not sure what the design intention is here.

There's a 5th bug also. I dont know if its just with PAX sivir (because thats the skin i have) but when you use boomerang, on the return trip it will go invisible sometimes and you will only be able to see the hit particle it makes.